Lower alkanoic acid esters of hyaluronic acid and the production thereof



kiliwiM-l Patented Dec. 8, 1953 LOWERTALKANOIG ACID ESTERS or" Hr- ALURONIC Acm AND THE PRODUCTION THEREOF Zareh-Hadidian; Needham, Mass, and Norman W. Pirie, Harpenden, England, assignors' to G. D. Searle & 00., Chicago, Ill.', a. corporation of Illinois No Drawing. Applicationlanuaryl d.1949, 1;

SerialN0.71,226 y x .8 Claims. (Cl. 260 '211- This invention relates to inhibitorsof the enzyme hyaluronidase, and to processes for preparing the same. It further relates to inhibitors of hyaluronidase prepared by chemical treatment of hyaluronic acid, particularly by acylation and nitration of hyaluronic acid and by de-acylation of acylated hyaluronic acid and denitrationof nitrated hyaluronic acid. .This application is a continuation-in-part of our copending application Serial No. 6,014, filed February 3, 1948. Hyaluronic acid is a mucopolysaccharide which constitutes part of the connective tissue of cells preferably carried outin the cold with fuming nitric acid. The reaction proceeds rapidly and can befarre'stedby the addition-of a large excess oiice. The addition ofice dilutes the acid,

' stopping the reaction and precipitating the acidins oluble nitrate. The-'acid-soluble nitrate remains-m solutionin the dilute nitric acid'and may be isolated by" neutralization, evaporation anddialysis. 7 The ratiofof aid-soluble to acid-insoluble nitrate varies from preparation to preparation. When'hyaluronic acid of low viscosity is used as the startingmaterialle. g., with a relative visof animals and humans. It is composed for the most part of glucuronic'acid and acetylglucosamine. A specific enzyme, hyaluronidase, exists in certain bacteria, venoms, 'spermatazoa, and

other s'ou'rces and plays a role in the process of invasion of cells and tissues by'depolymerization of hyaluronic acid, the ground'substance of conhective tissue. Hyaluronic'acid has been isolat ed with varying properties from umbilical cords, -skin, vitreous humor, synovial fluid, tumors and hemolytic streptococci.

Hyaluronidase is believed to take part in a I numbeiof important processes, including conception, and invasion by pathogenic organisms. 7

It is also believed to be a factor in rheumatoid arthritis, causing reduction in viscosity by bydrolysis or depolymerization of the ground substance of the human mesenchyme in which rheumatic processes are predominantly manifested.

' Inhibitors of the enzyme hyaluronidase are of value as contraceptives and for the prevention of invasion by micro-organisms, and also as possicovered that the substances obtained by de-acylating or denitrating such substances, as by re-.

:action with alcoholic alkali, are also hyaluroni- .dase inhibitors.

a {I'hepfocess' of nitration of nyaluromceeidfis' cos'ity of'l'A for' a l 'gram per liter solution measured in the presence of salt) there is little acidinsoluble product; I When even less Viscous fractions are used there is no acid-insoluble material at all; It ispbss'ible, therefore, that all the'acid-solublematerial is derived from the less viscous components of an initially inhomogeneous hyaluronic acid; It is unlikely that this is the sole origin; for if the acid-insoluble nitrate is driedby' sublimation and nitrated over again bythe method described, a further quantity of soluble nitrate is formed. Some degradation of the molecule during nitration is to beexpected, and this explanation of the originof some of the soluble nitrate is borne out by the increased proportion "of'profduct in that form if the nitration is continuediorlonger than 15 minutes.

The'sum. of the weights of nitrate in both forms is about equal topthestarting weight of hyaluronicxacid-andrwhen highly viscous hyaluronic acid used, 285% is'inthe ','acid- -insoluble form. .Nitr'ation generally leads .tosome' fall in the viscositYofhyaluronic acid. :The'extent of this fall is variable but ingeneral the "viscosity increment ofthfiaid-insoluble nitrate is about half that 'of' the parent hyaluronic acid. .The acids oluble nitratefis much. less viscous. 'Nitrated *hyaluronicacid; of both types, can usually be salted out from neutral solution by ammonium sulfate. 'With the acid-insoluble product, precipitation begins at about one-tenth of saturation and is complete at one-third of saturation.

' The more readily precipitated fractions are the more visco'us; and they are precipitated more ful alternative to neutralization, evaporation and dialysis in the preparation of acid-soluble ni.-

trates because, although the acid-insoluble nitrate is precipitated by saturated sodiumnitrate' 1 the soluble nitrates are not, and the: high nitrate concentration confuses ammonium sulfate precipitation. The nitrates contain about 6-11 of nitrogen and 4.5-7% of acetyL, I 4

sulfate from solutions containing no other component but it can be salted out if pyridine or some forms of protein are also present. The nitrates behave similarly for, although esterification of 4 wherein V is the relative viscosity at a concentration of 1 g./l., V is the relative viscosity at a given concentration, and C is the given concentration expressed in grams per liter.

Viscosity measurements are made in Ostwald viscosimeters at 25 centigrade. The standard ionic environment consists of 0.05 M sodium chloride and 0.05 M phosphate buffer at pH 7.0. Small variations. in salt, concentration in this region have little efiect onviscosity.

The loss of viscosity'of hyaluronic acid is used follow the course of hyaluronidase action. By the same method the effects of hyaluronidase inhibitors can be. observed. This method has the primary advantage that loss of viscosity is the first change that can be recognized during the enzymic decomposition of hyaluronic acid. The

. time reqpiredfor the viscosity to fall half way Hyaluronic acid is not salted out, b s-ammonium the hydroxyls has made the nitrates sufllcienth' hydrophobic to be salted out, they can be salted out at lower.- concentrationsof ammonium sulfate in the presence of pyridine:

Acetylation, ofv hyaluronic acid is most efficient? 1y achieved: by (1) treatment with acetic acid to cause: it to swell, followed by reaction with acetic anhydrideor acetyl chloride inthe presence of sulfuric acid, with warming, under certain circumstances where a product of high acetyl content is sought, or (2) treatment with formamide to cause swelling, fiollowed by acetylation in pyridine. The products made by the two methods vary somewhat in their properties, but all such substances have hyaluronidase-inhibitr ing qualities. While acetylation is simple and conveniently carriedv out and therefore i preferred, we also can acylate hyaluronic acid with other common acylating agents such as propionic anhydride, butyryl chloride. benzoyl chloride, henzoic anhydride and'the like. The. acyiated material. has an acyl content or about. 1.&*3.6% and a nitrogen content of about 24.5%..

De-acylation and denitration are preferably accomplished by reaction of the hyaluronic. acid derivative with alcoholic KOH or NaOH, generally at ordinary temperatures. Besides alcoholic alkali, methanolic potash, isopropyl alcoholic potash, and methanolic caustic soda may be used. Dilute solutions of alkali metal hydroxides in other lower alpihatic alcohols, as well as in water-soluble organic. solvents such as acetone and dioxane, can also be used for deesterification. De-acylation and denitration, by the foregoing methods, are referred to-herein as de-esterification. Esterification as used here n means the nitration and acylation of hyaluronic acids by the foregoing methods. The de-esterifled material has a nitrogen content of about 1.54% and an acyl content of 55-85%.

The term relative viscosity is used in this application to mean the ratio of the flow time of it given concentration of hyaluronic acid in a salt solution to the flow time of the salt solution alone. The term viscosity increment is the value of the relative viscosity minus one, and is a measure of the increase in viscosity due to hyaluronic acid. The relative viscosities are measured :at a concentration of 0.3 an. and converted to arconzcentrationof 1 g./1. by the follow ng iormule' I Va?! from the; initial. to the presumed final value has been taken'as: a measure of the rate of enzyme action. The measurement of half time is conventional in studies on hyaluronidase and has been adopted for convenience.

Since. no method exists for direct estimation of hyaluronidase, the course of the reaction between it and an inhibitor has to be followed by the indirect. method of determining the amount oi hyaluronidase that is made unavailable for thehyaluronic acid-hyaluronidase reaction in the presence. of the inhibitor or after the hyaluronidase has been exposed to the action of the; inhibitor for a givenperiod of time. If, then, one works in a region where there is a linear rela-. tionship between hyaluronidase concentration and, the rate of loss of viscosity by hyaluronic acid, one can consider this rate as a direct measure of the. amount of active hyaluronidase in the' system. The range over which such a relation exists varies with different preparations of hyaluronic acid tested at the same concentration. With; highly viscous preparations and with the partially purified enzyme preparation that we use. d via ion from n i y s ight up to enzyme. conc ation a/ h less viscous prepar tions th ra ge m y extend to, 5,0 mge/l. The following methods are used in estimating ibitory action: in instances where the l n th f exposure th e z to the in: hibitor is of little or no consequence, the enzyme is intrmducedinto a mixture containing both inibitor and substrate, and the subsequent ViS? eosity changes iollowed; here he extent of hibition is dependen on t e len t o pos r or the enzyme o he inhibi r. as n e s ofthe inhibition by serum, the enzyme and the inhibitor are. incubated together under the proper salt and pH conditions for a given length of time, then the. substrate is in roduced nto he m x.- ture, and the course of the reaction followed. The extent of inhibition is determined from the ratio of the. half time of the reaction with inhibitor, to that without. Thus a threefold inhibition (or an inhibition factor of 3) would be obtained in a half time of 600 seconds is obtained with inhibitor as compared with 200 seconds without. The reciprocal of this ratio is the fraction of. the initial enzyme concentration that is active. Partially purified bull testis enzyme is used in all these experiments.

:,Nitrates and acetates that have been made -from.viscoushyaluronic acid retain much of their initial viscosity. The effect of hyaluroni- -dase on them can therefore be tested in the usual way. The viscosity of nitrates is not reduced :ibyihyaluronldase and the viscosity of acetates often falls at first and then stays constant. We look on acetates behaving in this way as mixtures of material that can be attacked and material that is neither attacked nor inhibits the reaction.

The inhibition is measured by mixing suitable amounts of inhibitor with hyaluronic acid and then adding 50 micrograms of hyaluronidase per 4 ml. of solution. There is a slight increase in the inhibition if the enzyme and inhibitor are mixed first, but in this instance the extent of inhibition is not increased by allowing the enzyme and ester to be in contact for more than the time necessary for mixing. Some comparable results are collected in the table. Values are given for only one concentration of each inhibitor because the inhibition is proportional to the concentration of inhibitor. The table shows that acetates generally inhibit weakly, and the most active are partially acetylated products. On partial deacetylation the inhibition always increases. The results with nitric esters are more systematic; all of them inhibit. Attempts to get less nitration by using a smaller ratio of nitric acid to hyaluronic acid or by allowing the nitration to, proceed for a shorter time have led to less active products. The acid-soluble fractions from the'nitration of viscous material and the acidsoluble nitrates of non-viscous material are stronger inhibitors than the acid-insoluble nitrates. By suitably controlled removal of nitrate groups with alkali and alcohol the inhibitory power is substantially increased; but it is clear from the table that the intensity of the alkali treatment is of importance and that too drastic a treatment leads to a weaker inhibitor. For comparison the results of experiments with non-viscous hyaluronic acid and heparin are also included in the table. Many non-viscous preparations of varied origin have been tested and none has been found with a significantly greater inhibitory power than the one cited. Our testsare made at C; with hyaluronic acid having a relative viscosity of 7-8 for a 1 g./l. solution in 0.05 M NaCl and 0.05 M pH '7 phosphate buffer; although experimentsdescribed in the next paragraph show that there is more complete inhibition with smaller concentrations of phosphate. The same sample of dried partially purified hyaluronidase from bull testes was used throughout at 12.5 mg./l. Similar experiments have been made with larger and smaller concentrations of enzyme, at 37 C. and with samples of hyaluronicacid having a relative viscosity as low as 2 for the 1 g./l. solution. These variations in the conditions have not significantly affected the amount of inhibition observed.

Variations in phosphate and sodium chloride concentration, however, have a marked effect on inhibition by the esters. Several of these, including an acid-soluble nitrate, an acetate, a denitrated nitrate and a de-acetylated acetate, were tested in 0.05 M NaCl withphosphate concentrations varying between 0.013 M and 0.24 M; and in 0.05 phosphate with NaCl concen trations varying within the same range. Within this range there is an increasing inhibitory activity with decreasing salt concentration. None show a significant inhibitory activity in 0.05 M NaCl and 0.24 M phosphate and all show maximum activity in 0.05 M NaCl and 0.013 M phosphate; but they all follow different courses between these extremes. Products with identical inhibitory activity under our standard testing conditions may differ by a factor or two, at lower phosphate concentrations. 3

TABLE Concentra- Inhibition Description of Inhibitor tion in g. Factor Viscous hyaluronic acid acetylated by sulfuric method for 60 mins. 33% acetyl. 0. 1 1. 5 Above product tie-acetylated for 15 mins.

with 2 g./l. KOH. 14% acetyl 0.1 6 Viscous hyaluronic acid acetylated by suliuric method for 10 mins. 18% acetyl. O. 1 4 Acid-soluble product from nitration of viscous hyaluronic acid 0.01 3. 5 Acid-insoluble part of the same nitration 0. l 7. 3 Acid-soluble product from nitration of viscous hyaluronic acid 0. 03 3. 0 Acid-insoluble part of the same nitration 0. 03 2. 2 Abozfi insoluble product dcnltrated for 2 h.

0.07 g./l. KOH 0.005 5 2.5 g./l. KOH. 0.004 7. 5 7.5 g./l. KOH- 0. 03 2.2 Nitrated non-viscous hyaluronic acid 0.01 5 The same non-viscous hyaluronic acid be- J fore nitration 0. 1 2 Heparin 0. 1 2

In these experiments 2 m1. of a 0.6 g./l. solution of hyaluronic acid in 0.1 M NaCl and 0.1 M pH 7 phosphate buffer were mixed with 1 ml. of a solution of theinhibitor at four times the concentration specified in the second column. 1 ml. of a 50 mg./l. solution of hyaluronidase was then added and the flow time in an Ostwald viscosimeterwas measured at various intervals. The half time was found in the usual way and the amount of inhibition set out in the third column is derived by dividing the half time found in the presence of the inhibitor by that found in a control experiment with enzyme and subtrate alone. Our invention is further disclosed by the following examples, which are intended only as illustrations of our products and processes and which in no way limit our invention in spirit or scope. The parts are given as parts by weight.

Example 1 Dry hyaluronic acid (all samples tested do not, precipitate out of A -saturated ammonium sulfate solution, but precipitate out of alcohol), with the loose open structure that it has after drying by sublimation, is cooled in a freeiz ing mixture to about '10 C. Sixty parts of fuming nitric acid (specific gravity 1.59) also cooled to 10 C. are added and the mixture is maintained at -10 C. for 15 minutes with occasional stirring. All the hyaluronic acid dissolves in a few minutes. Three to four hundred parts of ice are now added with assiduous stirring. The temperature falls still farther and a white curd separates from a brilliant blue fluid. As soon as most of the ice has melted and all pockets of undiluted nitric acid in the curd have been broken up, the mixture is centrifuged for a few minutes and the solid is washed three or four times on the centrifuge with ice water. It is kneaded carefully each time to get rid of as much nitric acid as possible, and the washing is continued until the wash water can be neutralized by a drop or two of 0.1 N sodium'hydroxide. The solid is now suspended in water and brought into solution by adding enough NaOH to bring the pH to 6-7. This pale yellow, viscous fluid will be referred to as acid-insoluble nitrate.

All of the supernatant fluids are mixed and kept cold. They are neutralized with 20 NaOH with vigorous stirring and cooling so that the temperature never rises above 20 C. during the neutralization. The fluid, at pH 6, is concentrated by heating in a draft of air until sodium nitrate begins to crystallize out. It is then dialyzed for 10-20 hours to remove'most of the nitrate, concentrated again, and redialyzed. At this stage the solution from 100 mg. of hyaluronic acid has a volume of 2-3 ml. The solution remaining after thorough dialysis will be referred to as acidsoluble nitrate.

The nitrated hyaluronic acid preparations, when dried by evaporation, burn in a flash and their nitrogen content (Dumas) rises from 34% to 8.6%. If hyaluronic acid has the structure generally assigned to it, a chain of alternate glucuronic acid and acetylglucosamine residues connected by glucoside linkages, there are four free hydroxyls for each repeating disaccharide unit. The. sodium salt of the tetranitrate that could be made from such a substance would contain 12% of nitrogen and that of the dinitratc, 3.55%. Esterification of the -OH groups in this way does not apparently affect the N-acetyl group, for the acetyl content falls from 104.1% to 7-8%. The value to be expected for the dinitrate is 8.7%. Control experiments show that neither nitrous nor nitric acids, in amounts comparable to those present in a hydrolysate, are estimated as volatile acid after hydrolysis and distillation by the procedures used on these samples. On the other hand direct estimation, by the Elson and Morgan method (Biochem. J., 27:1824 [1933]), on the nitrated material shows an apparent disappearance of the glucosainiue. This result is due to the action of the nitric acid liberated during hydrolysis. The same disappearance can be brought about by hydrolyzing normal hyaluronic acid in the presence of a quarter of its weight of sodium nitrate-en amount corresponding to four nitrate groups Furthermore, de-esterifioation, by the method described in Example 7, restores the apparent glucosamine content and hydrolysis in the presence of a reducing agent such as hydriodic protects the glucosamine to a great extent from destruction. Fuming nitric acid probably acts to some extent as an oxidizing as well as a nitrating agent but it is clear that no oxidation involving the glucosamine is going on to an extent at all comparable to that found by Skanse and Sandblad (Acta Physiol. Scandinav. :37 [1943]) to accompany peroxide oxidation.

Example 2 A. A sample of hyaluronic acid obtained from pig umbilical cords (having a relative viscosity of 1.08, nitrogen content of 3.5%, acetyl assay of 7.7% and glucosamine content of 31.42%) is nitrated as in Example 1. The nitrated hyaluronic acid obtained by this procedure has an acetyl assay of 6.2% and nitrogen assay of 9.3%. It is insoluble in N/ 10 acid and /;-saturated ammonium sulfate solution. It is soluble in 80% aqueous alcohol and N/10 sodium hydroxide. It has a relative viscosity at 0.3 g./l. of 1.08 and a hyaluronidase-inhibition factor of 2 at a concentration of 0.03 g./l.

B. A sample of hyaluronic acid obtained from pig umbilical cords (relative viscosity 1.38, nitrogen 3.2%, acetyl 10.2%, glucosamine 37.9%) is nitrated as in A. The product has 7.3% nitrogen and is insoluble in N/10 acid and -satv.ratc-2d ammonium sulfate solution. It is soluble in 80% alcohol and N/ 10 sodium hydroxide solution. At a concentration of 0.03 g./l. it has an inhibition factor of 1.6.

C. Another sample of pig cord hyaluronic acid treated as in A gives a nitrated product of 6.4% nitrogen which is insoluble in ,maturated ammoniunr sulfate, solution and soluble in N710 acid, alcohol and Iii/'10. sodium hydroxide solution It. has. a. relative viscosity at: 0.3 g:./l. of 1.10 and: an inhibition. factor at. 0.03; g./l. of 51..

D. A sample of hyaluronic acid (relative viscosity-1.36). obtained fromhuman umbilical, cords is nitrated and worked up; according to Example 1, The nitrated material thus obtained has 10.2% nitrogen and is insoluble in VQ-saturated ammonium sulfate solution. It is soluble in 151110 acid, 80% alcohol, N/10 aqueous sodium, hydroxide and alcoholic alkali, eventually pr p ating: from the latter. It. has; a relative viscosity of 1.02 at. 0.3. gi/l. and an inhibition factQr 012' 4.5. at 0.03. g./1.

E. Another sample of human cord. hyaluronic acid (relative viscosity 1.5) treated asv in D gives a product of 4.9% acetyl and 6.9% nitrogen which is insoluble in N/ 10 acid. It is soluble alcohol, /;-saturated ammonium sulfate solution, N/l0 sodium hydroxide solution and alkaline alcohol; from the latter it eventually precipitates, as do the products of Examples 2A, 2B and 2C. It has an inhibition factor of 3, at: 0.03 g./l.

F. Pig cord hyaluronic acid (relative viscosity 1.15, nitrogen 3.6%, acetyl 7.8 glucosamine 29%) upon nitration as in Example 1 yields a nitration product having 6.0% acetyl, 4.7% nitro-. gen and which is soluble in N/ 10 acid, 80% alco-. hol, -saturated ammonium sulfate solution, N/l0 sodium hydroxide solution and alcoholic alkali, eventually prec pitating from the latter. It has a relative viscosity of 1.01 at 0.3 g./l. and an inhibition factor of 2.1 at 0.03 g./1.

Another sample of the same hyaluronic acid upon similar treatment gives a product of 6.5% acetyl and 5.9% nitrogen. The nitrated product is insoluble in N/ 10 acid and A i-saturated ammo-. nium sulfate solution. Itis soluble in 80% alco hol, N/ 10 sodium hydroxide solution and alcoholic alkali. Its relative viscosity is 1.11 at 0.3 g /l. and its inhibition factor is 1.5 at 0.03 g./l.

Example .3

Hyaluronic acid is swollen with acetic acid by adding glacial acetic acid in a thin stream to a 3-10 g./l. solution of hyaluronic acid. Mixing is complete until about 2 volumes have been added, after which precipitation begins and is substantially complete with 4 or 5 volumes. The mixture is centrifuged and the solid washed with acetic acid and used immediately. This precipitation does not lead to any significant fractionation of the hyaluronic acid, for only about 3% ofthe starting material is found in the solution when this is evaporated to dryness. This soluble fract1on has the normal nitrogen and g lucosamine content but its viscosity is low. The precipitate on the other hand, if dialyzed immediately, gives a solution with the original viscosity. 1

The fibrous clot of hyaluronic acid is pressed as free from acetic acid as possible and added to 200 times its weight of a mixture of 1 part of concentrated sulfuric acid, of acetic anhydride and of benzene. There is little or no solution of the hyaluronic acid, and, after a suitable interval, the mixture is centrifuged and the solid suspended in water and dialyzed. If acetylation is allowed to proceed for a, few minutes only the product has an acetyl content of'l6-20% after 10 minutes at 22 C. it rises to 25-33% and is not increased by longer acetylation at that temperature. By raising the temperature to 60" C. for 15 minutes, after acetylation has proceeded for times its weight of formamide.

9 an hour at 25 C., the acetyl content can be raised to 36%. :Acetyl determinations are made by hydrolyzing a sample for 75 minutes at 100 C. in 2.5- N H2804, steam-distilling the mixture and titrating the distillate'with N/70 NaOH, and include both O-acetyl and N-acetyl. Theoretical value for the tri-O-acetyl derivative of a polysaccharide built up from equal quantities of glucuronic acid and N acetyl glucosamine is 34% and for the tetra-O-acetyl derivative 39.4%. It would therefore appear that, as in the case of nitration, esterification remains incomplete.- Products that have been acetylated for a few hours only are still soluble in water over the whole pH range but those that have been acetylated at room temperature for many hours, or have been heatedto 60 C. during acetylation, are not soluble on the acid side of neutrality. There is a' progressive fall in'viscosity during acetylation.

Products acetylated for a few minutes only retain 70 80% of the originalviscosity incrementwh'ereas the tri-O-acetates retain only or less. 1

Example 4 A. Human cord hyaluronic acid (relative viscosity 1.30) is acetylated according to the procedure of Example 3 for'60 minutes at 25 C. and for minute at 55 C. The acetylated material is isolatedas in Example 3. It has acetyl and 2.4% nitrogen. It is soluble in N/10 acid, 80% alcohol and N/ 10 sodium hydroxide solution, and insoluble in /2-saturated ammonium sulfate solution. It dissolves in alcoholic alkali but precipitates therefrom in time. It has a relative viscosity of 1.02 at 0.3 g. /1. and an inhibition factor of 1.8 at 0.1 g./l.

B. Another sample of hyaluronic acid (relative viscosity 1.98) from human cords is acetylated as in A for minutes at 27 C. The product so obtained has 30%'acetyl and 2.3% nitrogen. It has a relative viscosity of 1.08 at 0.3 g./l. and an inhibition factor of 1.8 at 0.1 g./1.

C. Hyaluronic acid (relative viscosity 1.87, nitrogen 2.8%, acetyl 11.2% and glucosamine 41.7%) is acetylated by the method of Example 3 for 60 minutes at 27 C. The product thus obtained has 23% acetyl and 2.0% nitrogen. It is soluble in N/10 acid, 80% alcohol, N/ 10 sodium hydroxide and alcoholic alkali, precipitating eventually from the latter. It is insoluble in /zsaturated ammonium sulfate solution.' Its relative viscosity at 0.3 g./l. is 1.03 and its inhibition factor at 0.1 g./l. is 1.6.

D. A hyaluronic acid fraction (relative viscosity 1.98) from human cords is acetylated as in Example 3 for minutes 'at 27 C. The product has 18% acetyl, 2.4% nitrogen, and the same solubility characteristics as the material in Example 4C. Its relative viscosity is 1.32 at 0.3 g./l. and its inhibition factor is .5 at 0.1 g./l.

E. A sample of pig cord hyaluronic acid is acetylated as in Example 3. The acetylated material has 18% acetyl and 2.4% nitrogen. It is soluble in N/10 acid, 80% alcohol, -saturated ammonium sulfate, N/10 alkali and alcoholic alkali. Its relative viscosity at 0.3 g./l. is 1.04 and its inhibition factor at 0.1 g./1. is 2.0.

Example 5 I-Iyaluronic acid that has been dried by sublimation does not change its appearance when left for a few hours at 20 C. in formamide but at 40 C. it swells somewhat and at C. turns in an hour to a viscous dough when suspended in ten This dough can be mixed with an equal volume of pyridine by stirring for a few minutes. The plastic, rather than fluid, mixture is now mixed with half its volume of acetic anhydride, which causes an initial shrinkage but is incorporated into the mix-.

of iceand when brought to pH 2 with 5 N HCl,

v a soft curd separates. The fluid is dialyzed. If

acetylation has proceeded for an hour at 20 C. this acid-soluble product has an acetyl content of 14-16% while after 3 hours at 30 C.-it rises to 30%. In neither case has it any significant viscosity. The curd is not soluble at neutrality in the absence of salt and-is only partly soluble in the presence of salt; but it swells slowly to give a, suspension of gelatinous particles, which dissolve at pH 9-10. The solutions have onlya fifthof the viscosity of the parent hyaluronic acid. All these acetylated fractions coagulate with strong acid, and like the nitrates; they can be precipitated with ammonium sulfate.

Example 6 A. Hyaluronio acid of relative viscosity 1.3 from ,human cords is acetylated in formamide as in Example 5. The acetylated product contains 17% acetyl and 3.5% nitrogen. It is soluble in N/10' acid, alcohol and N/ 10 sodium hydroxide solution. It is soluble also in alcoholic alkali but precipitates therefrom eventually. It is insoluble in /;-saturated ammonium sulfate solution.

Its relative viscosity at 0.3 g./l. is 1.13 and its inhibition factor at 0.1 g./l. is 1.4.

B. A sample of hyaluronic acid from pig cords (Example 2F) is acetylated according to the methodof Example 5. The product so obtained assays 18% acetyl and 3.0-3.5% nitrogen. It has the same solubility properties as the product of Example 6A. Its relative viscosity is 1.04 at 0.3 g./l. and its inhibition factor at 0.1 g./l. is 1.7.

C. Hyaluronic acid of relative viscosity 1.3 from human cords is swollen in formamide and pyridine as in Example 5. The resulting mixture is mixed with one-half its volume of propionyl chloride and is stirred for 2 hours at 20 C. I It is then diluted with 4 volumes of ice and brought to pH 2 with 5 N "hydrochloric acid. The curd that separates is removed and the clear aqueous fluid is dialyzed. The dialyzed solution is evaporated to dryness under high vacum and at freezing temperature. The propionylated hyaluronic acid so obtained has little viscosity. It is soluble in N/ 10 acid, N/10 alkali and in 80% alcohol, but is insoluble in --saturated ammonium sulfate solution.

Example 7 The nitrates and acetates of hyaluronic acid can be partly de-esterified without extensive degradation by exposure to alkali in the presence of alcohol. Solutions of either ester containing 3-10 g./l. are mixed with ten volumes of alcohol.

mcee p mqucts. The. immediate purpose. of the; work themaking: of substances; that. inhibit hyalltmm. i'dase. is; however Satisfied.

m xa ple A- lin ni ated precinct or na ohq i KQH ma/1 o 9 53% m me; aicqhoi, /Z-SaFHrat QaInm nium sulfate- QQQLN lQ s fi m. di xide. t nsolub e a, h lica ka t itneaes y-iatedm t mf s-mnesA dc:

minutes, according to Example 7. The product so obtained contains 7.@% acety1 and 2.3% nitrogen It has the same solubility characteristics m -prams q xamplelfiAl Its. inhibf ijqn; ris 2.0a: 0.1 gJl; i

rop ies as the, product. oiEx mpleth. ltsrcl'',

ativefviscqsity at. a concentrati'Qn of 013; all. is; V 0.1, m is,1 i,; Ace yla e hy l'uronic ac d. Example 6 is de-esterifieci by'solutijon injalcoholic KQI-I, 2- 5/1.) f ri5. m nutes "l'h gde-a lated me: tel; i 'jhas 8.I%;acety1 'andv2 3%jnitrogenl Itjis sa able i'Nzm acid, 9% alc ho /2.-sai1 ed.i an; pnium suifatefan'd N/lq caustic. 'oluton" Itha's a relativegvisposityj o; LOQgat 0.3; g ari an n ibi ion. factor of 6 at 0-1: a/l.

i et on yeti meat ilif'a 'c o g KOBE 1 IQ f' inhibition: factor is 115 at jO l .11,

a p 4 dew r 'Weciaim;:;-- V j k; as a new composition or matter; a membet Qt? th arena cansis of a. lower alkanoicz acid este of; maln onij .1 and sa ts ther oi',. wheres n: t e; a xli cement, 1s lnjthe rang f: a msit $4. 72?- L a eweeimzo ition m r ar e-start 1m ante, wherein the a r ca s low allga-noy-l: radical, said composition, of at-1' t s nt he tan Qfi a a ein haract r zes bys s01:- w ex ndi tc'a k li and; 80% ab qmm ion or mat ac t la aw i ng: Ii-t sman e a hfiflfi hyalu QB?? 61.4. W 33. 15? wa qps sim- Qfi 9 m 1 s nd: en -ydr ies he ar s. ence of an acylation edip n of the group consisting of (a) sulfuric acid and (b) formamide and Pyridine, amt iselatina the. ester so forme 3 161 pro ess of: a ylating hyaluronic acid. whi h omprises: reactin hyaluronic: acid. with a lewera k n acid: anhydride in. the pres-- enceqian ny at medium of:- the roup: com I i e .cid and (12 1'- fnrmamide; and: py idine, an, iso vnew: the ester soiormett 6, T1353; process 0i; acet, lettin hyalumonie. acidi comprises, reamin hyaliiromiz'acid Wit-l air-hyd ide; t e: nn en e. 1? an. cylar:

i the atom consist ng of (a) 5111?;

an a sn .tinme-e ten c formea,

8. Th pl' m .'s..o ac ty atin hyaliirqnieacia which compris dwith reactin hazel-uremic aci.

ciri'ql inthe: presence of; f rmantide he and; 1 -se aiizna the estervsaaformea:

V Z AREH,

V Qi e r s-fiber. ler-Qt 1 his atent GhemV Abs, vol. 351 (194.15); page-370x13. NationaL- 13 1112.; ofr; Standards Polarimetry; Seaman-mam, and the Sugars, Ciro;- (3M0; 1942, pages 435-487. 

1. AS A NEW COMPOSITION OF MATTER, A MEMBER OF THE GROUP CONSISTING OF A LOWER ALKANOIC ACID ESTER OF HYALURONIC ACID, AND SALTS THEREOF, WHEREIN THE ACYL CONTENT IS THE RANGE OF ABOUT 14% TO 36%. 